For operating an LED (light-emitting diode) a predetermined voltage has to be applied to the LED to drive a defined current through the LED. The voltage is usually generated by an electric driver circuit, such as a flash-LED-driver. The electric driver circuit comprises an input terminal to supply a voltage supply potential. The input terminal may be connected to an electric path comprising an external voltage supply source and an inductor. The electric driver circuit may comprise a first output terminal to output a first output voltage and a second output terminal to output a second output voltage. The electric driver circuit may comprise a current sink/source being connected between the first and second output terminal. A capacitor may be connected to the first output terminal. The second output terminal may be connected to the LED.
The electric driver circuit may be configured as a boost converter which is activated to provide the predetermined voltage for operating the light-emitting diode, when the voltage on the current sink/source between the first and second output terminal drops below a certain voltage, for example 200 mV. When the electric driver circuit is operated in the activated state, the output voltage at the second output terminal is regulated to a predetermined value to drive a predefined current through the light-emitting diode. The electric driver circuit is activated, for example, when the voltage generated by the external voltage supply source falls below a threshold value caused, for example, due to a discharge of a battery coupled to the input terminal of the electric driver circuit.
Assuming that the current through the light-emitting diode is slowly ramped up, it can happen that the electric driver circuit has to be activated at very low LED-current, but it can also happen that the electric driver circuit has to be activated at a very high load. This depends on the charge/discharge state of the external voltage supply source, for example a battery, the generated voltage at the second output terminal, the series resistance of the battery, the series resistance of the inductor or other inherent resistors of the electric driver circuit inside a housing of a chip including the electric driver circuit.
After being activated to regulate the output voltage at the second output terminal to the predetermined value, during a first cycle of a regulation operation mode of the electric driver circuit, a first current path of the electric driver circuit in which a current flows from the external voltage supply source through the inductor/coil to a reference potential of the electric driver circuit is activated. During a subsequent second cycle of the regulation operation mode of the electric driver circuit, the first current path is deactivated and a second current path is activated in which the current flows from the inductor to the first output terminal of the driver circuit to charge the external capacitor.
When the output voltage at the first output terminal is at the same level as the voltage of the voltage supply source coupled to the input terminal of the electric driver circuit, the current/energy which was generated in the inductor within the first cycle of the regulation operation mode cannot be discharged within the second cycle of the regulation operation mode to the external capacitor connected to the first output terminal. This causes a huge coil current peak in the inductor, and therefore a huge battery current peak. These current peaks may cause unexpected shutdown of mobile devices including the light-emitting diode, such as a flash LED module, due to the high battery current consumption. Therefore, such peaks of current in the inductor have to be avoided, especially in high current flash-LED-drivers.
It is desirable to provide an electric driver circuit for driving a light-emitting diode in which the occurrence of a huge coil current peak or a huge battery current peak during a regulation operation mode of the electric driver circuit to generate a predetermined output voltage to drive a predefined current through a light-emitting diode may be avoided. There is also a need to provide a method for operating an electric driver circuit for driving a light-emitting diode which enables to avoid a huge coil current peak/huge battery current peak during a regulation operation mode of the electric driver circuit to generate a predetermined output voltage to drive a predefined current through the light-emitting diode.